The invention relates generally to electrical devices having magnetic cores, and more particularly to electrical transformers.
One typical example of an electrical transformer includes one or more convolutely or concentrically wound magnetic cores. In this type of transformer, the magnetic core may be formed from a number of radially adjacent lamination strips of magnetic material. The strips may be cut to precise lengths, which are incrementally adjusted to compensate for the radial build of the core, assembled into a circular configuration and then pressed into a generally rectangular or quadrilateral shape having a window opening extending axially therethrough.
Each circular laminated core is pre-shaped to a final generally rectangular or other quadrilateral configuration, restrained in this shape, and then annealed to relieve internal mechanical stresses resulting from the shaping process. After shaping and annealing, the core or cores are assembled or "laced" through a pre-wound coil assembly which includes both high voltage and low voltage windings. The lacing procedure involves removing the innermost group of laminations from the annealed core structures and inserting the cut ends of the laminations through the opening in the coil assembly. This process is repeated with intermediate groups of laminations until the outermost laminations have been laced into the coil assembly. Thus, in the finished coil and core structure, the high and low voltage windings extend through the window openings in the magnetic cores, and the cores extend through a window opening in the coil assembly.
In another type of transformer, each of one or more magnetic cores is comprised of a series of axially stacked laminations. In such a configuration each lamination may be stamped or die-cut in a one-piece or multi-piece configuration having a generally rectangular or other quadrilateral shape, with a window opening extending therethrough. The laminations are serially stacked in an axially adjacent arrangement, through the window opening of one or more coil assemblies.
Although electrical transformers of the types described above have proved to be quite reliable and efficient, the present invention provides for a significant improvement in the performance characteristics of such transformers by decreasing both the losses through the core and the amount of material needed to fabricate the core. The window opening extending through a core constructed in accordance with the invention has a corner at the intersections between the outer leg portion and the upper and lower yoke portions that is more gradually curved than the corner at the intersections between the inner leg portion and the upper and lower yoke portions. Such a configuration significantly improves the space utilization factor of the transformer core window, thereby shortening the magnetic path length and decreasing the amount of magnetic material required to fabricate the core. The more gradually curved outer window corners also contribute to the ease of lacing the core laminations into the coil assembly by making it easier to align the serially inserted groups of laminations. Such ease of insertion into the coil assembly therefore reduces the mechanical stresses placed upon the previously annealed core during assembly. Such ease of assembly reduces the amount of mechanical strain (and the resultant increased losses, termed "destruction") suffered by the magnetic core material during assembly, thereby increasing the efficiency and performance of the transformer. Alternatively, both the inner and outer window corners may be gradually curved if resilient or extensible insulating materials and winding from materials are used, for example.
According to a preferred method and apparatus for manufacturing or forming the magnetic core according to the invention, a quantity of magnetic material is formed into a generally toroidal configuration. At least one forming member, and preferably an assembly of a pair of said forming members, are inserted into the opening extending through the toroid of magnetic material. The forming members have first and second forming surfaces that are separated by window corner-forming surfaces of a predetermined shape for forming the desired window corner shape and configuration as described above.
First portions of the magnetic are material forcibly deformed against the first forming surfaces of the forming members, preferably by compressing the first portion between the forming members and corresponding first forming die plates located on opposite sides of the toroidally-shaped magnetic material. Similarly, second portions of the magnetic material are preferably deformed by being compressed between the second forming surfaces and corresponding second die plates on opposite sides of the toroidal magnetic material. During the deforming of second portions the magnetic material is urged against the window corner-forming surfaces to form the window corners with great precision to the predetermined and desired configuration.
The forming members, in the preferred embodiment, are generally U-shaped or channel-shaped end plugs. The base of each end plug has the first forming surface on its exterior, and the spaced legs of the end plug have the second forming surfaces on their exteriors, with the corner-forming surfaces therebetween. Preferably, a pair of first force-applying mechanisms, which may be hydraulic or pneumatic cylinders, for example, are equipped with forcibly extendible members for urging the first die plates against the magnetic material. The first force-applying mechanisms also include anchoring structures for holding the end plugs in place at a fixed position relative to the force-applying mechanisms when the first portion of the magnetic material is compressed. When the second portions of the magnetic material are deformed, the preferred first force-applying mechanisms and the end plugs slidably move apart and spacer members are inserted between the end plugs to preserve the desired core shape until after the core is annealed.
Additional advantages and features, as well as additional embodiments and variations, of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.